To better understand why bats are the only mammals capable of sustained flight, a team of biologists at Brown University is examining ultra high-speed X-ray videos of fruit bats as they launch themselves into the air.

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Led by Nicolai Konow, the team used X-ray Reconstruction of Moving Morphology (XROMM), a technology that integrates 3D renderings of the bones with the X-ray video, in their study of Seba’s short-tailed bat. The finding was a bit of surprise. Conventional wisdom holds that small mammals have stiff, thick tendons that cannot be stretched. But the X-ray videos showed that the bat actually stretches the tendons that anchor their biceps and triceps muscles to their bones, the compress the tendons, releasing energy to help their flight after takeoff.

This finding was confirmed using fluoromicrometry, a system in which chemical markers are injected into the bat's muscles, allowing the researchers to measure the changes in muscle length during expansion and contraction.